Ultrastructural observations on the third-generation merozoites of Eimeria tenella in chicks.

The fine structure of the third-generation merozoites of Eimeria tenella is described from caecal enterocytes of chicks 120 h after experimental infections. The merozoites conformed to the general eimerian pattern except that they were bounded by two unit membranes. Young gamonts also conformed to the general eimerian pattern, and were limited by an outer unit membrane and an interrupted inner membrane. Enterocytes invaded by third-generation merozoites showed a loss of microvilli and large blebs that protruded into the caecal lumen. These blebs appeared to contain only cytoplasm and not any cell organelles.